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Wireless Power Transfer - short range

Former Member

Hey everyone,

I'm new to this forum, looked around a little but didn't find what I was looking for. So here's my question, maybe someone has experience in similar stuff.

I am planning to build a series of small plastic toys/figures that would light up from the inside (transparent plastic) when placed on their substrate, and dim when lifted higher than let's say 10mm. So basically what I am looking for is some sort of small inductive coils and surrounding components that would do the job and transfer enough energy to light up one SMD LED at a short range.

I want to place the coil and an LED inside the toy (on it's bottom), and another coil and other components inside the substrate.

Dimensions: The figure's bottom has only 25 mm radius (So the receiving coil can be 25mm max in radius, the smaller the better!). The substrate is a bit larger, around 35mm (So the transmitting coil can be 35mm max, also the smaller the better).

I did a little research, and it seems like all the coils are much larger than 25mm. Saw some projects on the internet where people build coils to light up LEDs at home, but those are too big aswell.

Another question is, what frequency should I choose for the best performance? Again, I'm not interested in increasing the range, quite the opposite, I want it to start dimming almost the moment I lift the toy from the substrate.

 

Thank you very much in advance for your answers, any help is much appreciated!

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  • Hello Andriy,

     

    This is what I did for the previous Wireless Power Solution challenge: Ultrasmall Qi LED HACK

    I designed the board myself, you'll be abel to find the Eagle file here: My entry; the videos AND the EAGLE files. Yes, the TI Wireless charging kits are expensive, but can transfer more power, and especially at a higher efficiency, than toothbrush chargers. The components in itself are not that expensive, which is the cost you'll be looking at eventually (for reference, this is how low you can go with the transmitter circuit: http://www.aliexpress.com/cheap/cheap-charger-circuits.html). Another safety feature that you'll want to have is 'Foreign Object Detection' -> because you'll use a flat surface, any metal object will be heated by induction. In the Qi standard the charged object and the charger communicate with each other, and detect energy loss. In toys that might prevent some seriously hot keys on a playing surface....

     

    The coil is still reasonably large, in the 'Ultrasmall Qi LED Hack' post, but more coils are available at several vendors. Of course I'd like to promote Wuerth, but I think they don't have a coil that is that small. I've seen the device on http://www.wpcentral.com/exploring-future-wireless-charging-now-qi-mwc (the 'PowerKiss'), and I think that's the smallest certified device I've seen. Of course you can also  roll your own coil, and not be officially Qi compliant.

     

    By the way; why is this in 'Open Source Hardware'? You could better ask this in Wireless Power Solution , Experts ....

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  • Hello Andriy,

     

    This is what I did for the previous Wireless Power Solution challenge: Ultrasmall Qi LED HACK

    I designed the board myself, you'll be abel to find the Eagle file here: My entry; the videos AND the EAGLE files. Yes, the TI Wireless charging kits are expensive, but can transfer more power, and especially at a higher efficiency, than toothbrush chargers. The components in itself are not that expensive, which is the cost you'll be looking at eventually (for reference, this is how low you can go with the transmitter circuit: http://www.aliexpress.com/cheap/cheap-charger-circuits.html). Another safety feature that you'll want to have is 'Foreign Object Detection' -> because you'll use a flat surface, any metal object will be heated by induction. In the Qi standard the charged object and the charger communicate with each other, and detect energy loss. In toys that might prevent some seriously hot keys on a playing surface....

     

    The coil is still reasonably large, in the 'Ultrasmall Qi LED Hack' post, but more coils are available at several vendors. Of course I'd like to promote Wuerth, but I think they don't have a coil that is that small. I've seen the device on http://www.wpcentral.com/exploring-future-wireless-charging-now-qi-mwc (the 'PowerKiss'), and I think that's the smallest certified device I've seen. Of course you can also  roll your own coil, and not be officially Qi compliant.

     

    By the way; why is this in 'Open Source Hardware'? You could better ask this in Wireless Power Solution , Experts ....

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